Electrical treating apparatus, especially for sterilization



Oct. 11, 1938. F. s. SMITH 2,132,704

ELECTRICAL TREATING APPARATUS, ESPECIALLY FOR STERILIZATION Filed Oct. 8, 1934 INVENTOR.

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ATTORNEYS Patented Oct. 11, 1938 PATENT OFFICE ELECTRICAL TREATING APPARATUS, ESPECIALLY FOR STERILIZATION Franklin S. Smith, New Haven, Conn.

Application October 8,

11 Claims.

This invention relates to apparatus which is particularly adapted for electrically sterilizing food products and the like and for destroying insect life, such as eggs, larvae, pupae, and the like.

One of the objects of the invention is to provide a simple, inexpensive and thoroughly practical apparatus which may be used among other things for subjecting food and other products to electric treatment for destroying life, such as the above-mentioned insect life. Another object is to provide an apparatus of the above-mentioned character in which simplification of construction, particularly of electrical insulating difficulties, may be dependably achieved. Another object is to provide an electrical sterilizing apparatus in which protection and safety against high voltages may be facilitated. Another object is to provide a construction of the above-mentioned character in which certain advantages of electronic conduction devices may be achieved while also dependably improving the operating characteristics and conditions of the latter. Other objects will be in part obvious or in part pointed out hereinafter.

, The invention accordingly consists in the features of construction, combinations of elements,

and arrangements of parts as will be exemplified in the structure to be hereinafter described and the scope of the application of which will be indicated in the following claims.

In the accompanying drawing, the single figure shows a front elevation, partly diagrammatically and partly in vertical central section, of an illustrative embodiment of the mechanical and electrical features of my invention.

Referring now to the drawing, and for purposes of greater clarity of description, it may be assumed that the products to be treated are packaged food products, such as milled cereals, for example, contained in packages, such as the packages I, and that the thus packaged products are to be subjected to the above-mentioned electrical sterilizing treatment; accordingly, I provide a conveyor, illustratively in the form of a belt ll, of suitable length, along or by which the packaged products in may be moved at a suitable rate of speed and into the treatment zone.

The belt II, which is made of any suitable non-conductive material, such as canvas, cotton, or the like, extends over pulleys or drums l2, I3 rotatably mounted in suitable standards |4-l5 extending upwardly from and at the respective ends of the frame, generally indicated at l6, of the apparatus.

1934, Serial No. 747,438

Any suitable means may be provided for effecting movement of the conveyor belt II and illustratively I may employ a motor ll connected to the drum I3, by a driving connection l8 for driving the drum l3 in clockwise direction, and hence 5 for effecting movement of the conveyor belt II with the packaged goods ID carried thereon in a direction from the left to the right.

Any suitable means may be provided for sustaining the upper side of the belt [I against sagging under the weight of the products to be treated; illustratively, I may provide a sheet or plate-like member l9 extending underneath the upper side of thebelt H from drum l2 to drum l3, thus in effect forming a table, being made' of any suitable solid dielectric material, such aslaminated Bakelite. It may be supported in any suitable manner, illustratively by a pair of substantially similar side beams 20 extending between and supported by the respective pairs of standards I l-l5 at the ends of the frame.

Along the product-carrying or upper side of the belt l I I may provide as many treatment zones or treatment apparatuses as may be desired and these may, and preferably do, take the form of the apparatus shown in the drawing and about to be described, providing illustratively, but not by way of limitation, one treatment zone. This apparatus is to produce a ribbon of electric discharge preferably in the form of a corona-like discharge, through which the conveyor ll moves the products l0 and since relatively high voltages are involved in this apparatus and since certain parts thereof are at correspondingly high voltages, the matter of achieving effective and safe insulation of these parts in a simple, inexpensive but thoroughly practical manner, is one of the dominant aims of my invention.

Considering first the physical parts of this discharge-producing apparatus, I provide an auxiliary frame Ili of any suitable construction and mounted by any suitable means for adjustment in a vertical direction, as viewed in the drawing. This frame Iii is preferably made of metal and illustratively may be slidably mounted in suitable vertical uprights IB and I6 supported upon base [5. Suitable adjustment of the auxiliary frame I6, in a vertical direction and hence toward or away from the conveyor belt II, is achieved by, for example, elevating screws 2|- 22 operated through a suitable train of driving gears generally indicated at 23 and controllable at will as by the hand-wheel 24. All of these parts may be fabricated of any suitable metal parts and it is to be noted that all of these parts 55 are at ground potential, being conductively connected to the base I6 which is grounded in any suitable manner.

The auxiliary frame It extends over the products-carrying belt II and supports certain low potential parts of the electrical system and apparatus that produces the discharge in the treatment zone which is intersected by the belt I I and the products carried by it. These low potential parts include a plate-like conductive member 25 which is effective, as will be more fully explained hereinafter, to form part of a condenser or capacitative electrical circuit. Since, for reasons later set forth, the member 25 is to be rotated, I prefer to make it in the form of a disk and attach it, in any suitable manner, to the shaft 26 which is driven by any suitable means at a suitable speed and preferably and illustratively is the shaft of an electric motor 21.

Motor 21 may be of any suitable type and is supplied with electrical energy from any suitable source. Illustratively, it may be a polyphase motor, being supplied with energy from the polyphase circuit A through suitable connections B including a switch C. The source of electrical energy and hence the motor 21 itself may be of any suitable voltage, preferably the usual relatively low voltages available in ordinary power supply circuits. The frame of the motor 21, however, being secured to the auxiliary frame I 6 will be seen to be grounded, and thus the electrode disk or plate member 25 is likewise effectively maintained at ground potential. The disk 25 is of a diameter generally commensurate with the width of the conveyor II, but preferably is slightly less than the width of the latter.

Juxtaposed to the driven plate member 25 and likewise disk-like in shape and hence presenting an area commensurate with the area of the disk 25 itself, is an electrode disk 28 positioned, however, underneath the product-carrying orupper side of the belt II. This electrode disk 28, however, is maintained at a relatively high potential, illustratively a potential on the order of 150,000 volts, and in so far as certain features of my invention are concerned any suitable means may be provided to maintain the electrode 28 at such a high potential.

Preferably, however, and in order to lessen the need for insulation at such high voltages, as well as to simplify the insulation required and to increase the safety factor of the apparatus, I provide a transformer 29-410 and position it underneath the electrode disk 28 and hence within the confines of the vertical and lateral dimensions of the apparatus.

This transformer 2930 is preferably of a construction like that disclosed in my co-pending application, Serial No. 747,436, filed October 8, 1934, and to which reference may be made for its details of construction; this transformer includes a low voltage winding 30 and a high voltage winding 29, related to a suitable core diagrammatically indicated at 3 I, all contained within a casing 32, the latter being preferably cylindrical, with its axis extending vertically. In line with its vertical axis and at the upper end thereof the casing 32 carries a suitable high voltage insulating terminal or bushing 33 which may take the form disclosed and described in my abovementioned co-pending application, and, while one terminal of the high voltage winding 29 is grounded as at 34, the other is carried out of the casing 32 through the high voltage insulator 33 as by the conductive member 35 extending vertically therethrough, whence it is connected to the electrode disk 28.

As above noted, the electrode disk 28 is underneath the upper side of the conveyor belt II; it may be supported in that position in any suitable manner, for example, as by brackets 36 secured to the insulating side beams 20 though I may, if desired, dispense with such supporting arrangement of the electrode disk 28 and support it by the insulating high voltage terminal construction 33 carried by the transformer casing 32 and such support I may achieve by extending the conductive member 35 upwardly, member 35 being of suitable rigidity and strength and having the electrode disk 28 secured thereto in any suitable manner, as at 31. In such case the transformer and terminal construction and electrode disk 28 form, it will be seen, a compact unit.

As will be seen in the drawing, the casing 32 of the transformer is supported on the base I6 on suitable legs or standards 38 by which the casing and hence the one terminal 34 of the high voltage winding 29 are grounded to the base It and by which, also, the casing 32 is held upwardly spaced from the base I6; through the space between the transformer casing 32 and the base I6, is passed the lower side II of the conveyor belt II, suitable idlers or drums 39 and 40, rotatably supported on the base I6, being provided to guide the belt in this path.

The top plate or table I9 of the belt support is preferably interrupted in the treatment zone in order to provide therein, but alined with the plate-like member I9, an insulating member II having more suitable dielectric properties for better achieving the desired action in the treatment zone itself; the solid dielectric member 4| is preferably in the shape of a disk, fitted into a round opening in the plate member I9 and is made of Pyrex glass or quartz; it is preferably of somewhat greater diameter than that of the high voltage electrode disk 28 and is provided with a peripheral and downwardly extending flange M thereby materially to elongate the possible leakage path from the high voltage electrode 28 to the supporting structure 20-20 and I9 or to its other parts.

The solid dielectric member II may be supported in any suitable manner and preferably with its upper face in the same plane with the face of the plate-likemember I9, thereby to form a smooth and plane surface along which the conveyor belt II is moved. It may be supported in that position in any suitable manner, preferably detachably, so that it may be replaced, and illustratively I may provide rests or brackets 42-43 secured to the side beams 20--20. These brackets 42-43 are preferably adjustable in a. vertical direction so as to accommodate any desired thickness of member 4I while keeping its upper face in the plane of the belt II and similarly brackets 3636 as well as the connection 31, are adjustable to permit the electrode disk 28 to be adjusted vertically in relation to the dielectric member 4I. The parts M and 28, moreover, are preferably parallel to each other and in contact with each other, and the several adjustable devices just mentioned are constructed accordingly.

The electrode or plate member 25, rotated as by the motor 21, is provided with depending or downwardly directed individual electrode members 44, suitable in number and suitably distributed throughout or about the under face of the rotating electrode plate 25; by way of illustration, but not by way of limitation, I have shown these members 44 arranged in a ring or circle throughout which they may be staggered if desired, or throughout which they may be alined,

being suitably spaced from one another as is generally indicated in the drawing. In general they form a ring or circle whose diameter is commensurate with the width of the belt I I.

In so far as certain features of my invention are concerned, the members 44 may be made of any suitable and preferably conductive material butpreferably they are in the form of sealed tubes of, for example, glass, within which electronic conduction may take place. For example, they may contain a suitable gas, such as neon, for example, at relatively low pressure (several millimeters, for instance) and at their upper ends,

4 where they are exteriorly secured in any suitable manner and preferably detachably to the disk member 25, they are each provided interiorly with a small electrode (see the sectioned member 44 in the drawing) which is electrically connected or grounded to the supporting electrode disk 25.

When suitably stressed, as will later more clearly a pear, the column of gas within the conduction devices 44 becomes ionized and hence becomes electrically conductive.

As the motor 21 rotates the electrode disk 25 at a suitable speed, a speed suificient to give the members 44 a linear speed of say 1500 feet per minute, the latter are therefore swept about their circular path above the products l0 carried by the belt II at a suitable speed on the order of 15 feet per minute, motor 21 and electrode disk 25, as well as the electrode members 44, being substantially at ground potential. The high voltage electrode disk 28, however, is at a potential on the order of 150,000 volts, as above noted, and preferably this potential is a high frequency alternating potential, the transformer 2930 having an appropriate ratio of transformation to provide this high potential to the electrode disk 28.

The high frequency alternating energy supplied to the low voltage winding 30 of the trans- ,former 2930 may be obtained in any suitable plied to the high voltage electrode 28 may be on the order of 640 cycles per second, and the alternator 46 is, of course, of corresponding frequency.

Accordingly, with the electrode plate member 25 at ground potentialand the electrode disk 28 .at high potential, the dielectric therebetween becomes stressed, but the dielectrics are so proportioned to each other that complete breakdown thereof does not take place and rupture is localized and confined preferably to a corona-like discharge in the region or space between the plane of the lower ends of the moving conduction devices 44 and the plane of the upper face of the dielectric member 4|; the dielectric stress produced by the potential difference applied to the electrode disk members 28 and 25 effects ionization of the gaseous content of the conduction devices 44, the columns of gas therein become conductive, and the lower ends of the devices 44 are thus made effective accurately to concentrate, localize, or control the corona-like discharge into what is virtually a dense annulus (luminous and visible to the eye) in the space between the two above-mentioned planes. Through this annulus the product to be treated is moved by the conveyor belt H, preferably along a, diameter or cord of the annulus and hence so that each product or particle thereof to be sterilized passes twice through the discharge.

Where the product is packaged and due to the rotation at relatively high speed of the conduction devices 44, the discharge is swept onto the product in the package at one side or vertical face of the package and off of another as the package passes through one portion of this annulus of discharge but this action is reversed, due to the traverse in reverse direction of the devices 44 relative to the path of movement of the packaged product, as the packages pass through the other side of the annular discharge; by such actions as these effective and dependable and uniform treatment and sterilization of the contents of the package or packages are achieved.

The detailed electrical or sterilizing action upon the insect life within the products to be sterilized is substantially thisz-It may at this point be noted that the packaged material, such as corn-meal, flour, or the like, and assumed to be contaminated with insect life, may be considered as a heterogeneous dielectric made up of various dielectrics in series multiple arrangement and containing isolated capacities, the latter being the contaminations represented by the various stages of insect life. If the material is packaged, the pasteboard, paper, or the like, of the package itself, constitutes a dielectric of one permittivity, the individual particles of the meal, flour, or the like, constituting a dielectric of still another permittivity, and the air intervening these particles constitute still another dielectric but one of lowest permittivity of all, namely, unity. When this heterogeneous dielectric enters the treatment zone, the dielectrics of higher permittivity cause overstressing of the air dielectric with resultant ionization and breakdown thereof. The contaminating particles, such as insects, eggs, larvae or pupae thereof, are, however, of substantially infinite permittivity and are in effect conducting so that the corona streamers virtually seek out and pass through these contaminating particles and thus effectively bringing about their destruction.

Preferably the devices 44 carried by the rotating electrode member 25 do not extend truly vertically but rather are inclined to the vertical so that, with the structure 25-44 rotating in the direction of the arrow (counter-clockwise, as viewed from above), the lower or trailing end of each member 44 lags behind the upper end thereof; where the tubes 44 are cylindrical, this inclined relation results in making the effective cross-section thereof, so far as air resistance is concerned, virtually oval and hence somewhat stream-line, thereby minimizing the setting up of eddy air currents or other air disturbances, particularly at the lower ends thereof where the eflective control of the discharge is concentrated, and thus disturbance of the discharge itself by air disturbances is minimized. Furthermore, the relatively rapid linear movement of the conduction devices 44 results in sufiiciently rapid transfer of heat therefrom to the surrounding air, and thus possible over-heating is precluded.

The relatively high frequency of the high potential applied to the electrode disk 28, on the order of 640 cycles per second, insures such a high number of peaks, per unit time interval, in the high voltage wave that, coupled with a number of devices 44 and their rapid movement, the above-described annulus of corona-like discharge is of substantial density and uniformity to achieve effective sterilization.

As above noted, I prefer to preclude complete rupture or breakdown in order thereby to avoid possibility of puncturing the material of the package itself; instrumental in achieving this action is the condenser or capacity action brought about by the solid dielectric 4|. For example, the latter is of sufiicient dimension and dielectric properites that. the condenser or capacity, formed between the electrode disk 28 on the one hand and the portion of the discharge annulus where the latter impinges upon the belt or upon the dielectric member 4|, does not break down even under the maximum voltage of the transformer winding 29. Accordingly, dependable corona-like discharge through the product undergoing treatment may be achieved with adequate safeguarding of the material of the package, such as pasteboard, or the like, where the product is packaged.

By the same or similar action, and particularly where the spacing between the devices 46 and the belt is not too small in proportion to the voltage of the transformer winding 29 and other factors, I insure the continued and steady production, in the treatment zone, of the above-mentioned corona-like discharge. I may, however, under certain requirements of practical use, lessen this spacing between the electronic conduction devices 44 and the plane of the belt ll so as to make more intense the individual corona streamers emanating from the indivdual electrode devices 44, though lessening the number of the streamers.

In any case, however, I prefer to insure against complete disruption or breakdown in the high potential circuit by proportioning the condenser formed between the belt I l and the electrode disk 28, with the intervening solid dielectric 4 l so that it can per se safely withstand the potential of the system, it being borne in mind that, with the breakdown of the dielectric between the devices 44 and the belt l l with the resultant formation of theannulus of corona discharge, the condenser of which the solid dielectric 4| is the dielectric, is subjected to a relatively large fraction of the total voltage of the system.

By manipulating the hand-wheel 24, the motor 21 with its electrode structure may be raised or lowered, thus setting the apparatus for the accommodation in the treatment zone of different thicknesses of product or for different dimensions of packages. I may vary the capacitance of the condenser or condensers of which the solid dielectric 4|; forms a part by replacing the latter by a member similarly shaped but of difierent material, or of the same material but of different thickness. Thus I may vary or control the character or intensity of discharge, particularly of the individual streamers of the corona discharge in the treatment zone, to suit the particular practical conditions to be met.

By the mechanical and electrical arrangement of parts above described, a very practical and safe simplification of the electrical insulation is achieved without impairing dependability of action of the apparatus. Also, substantial compactness of construction is achieved, and saving in material and reduction of cost of construction flow therefrom.

It will thus be seen that there has been provided in this invention an apparatus in which the several objects hereinbefore set forth, together with many thoroughly practical advantages, are successfully achieved.

As many possible embodiments may be made of the above invention, and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth, or shown in the accompanying drawing, is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In electrical treating apparatus, in combination, a source of relatively high potential, one side of which is grounded, moving electrode means having connected thereto driving motive means,

from which a discharge may emanate and all at ground potential, a conveyor belt for bringing a product to be treated into the discharge region of said electrode means, there being on the under side of said belt and juxtaposed to said electrode means a solid dielectric member onto which the discharge impinges, means underneath said solid dielectric means for housing said source of high potential and having a high potential terminal related thereto, and conductive means adjacent the under side of said solid dielectric means and supported by said high potential terminal.

2. An apparatus like that of claim 1 in which the motive means is an electric motor supplied with energy from a suitably relatively low voltage circuit, the grounding of the motor and of one side of said high potential source protecting the low voltage circuit against the high potential.

3. An apparatus like that of claim 1 in which the source of high potential is a high voltage transformer and the means housing the source is a transformer casing, the high potential terminal being supported by the latter.

4. An apparatus like that of claim 1 in which the moving electrode means rotates and hence is driven in a circle by the motive means, and in which the conductive means supported by the high voltage terminal is in the form of a disklike plate electrode.

5. In electrical treating apparatus, in combina tion, a conveyor belt supported by spaced drums and having an upper product-carrying side and a lower return side spaced from the upper side, spaced discharge-controlling means, one above the upper side of the belt and the other underneath the upper side of the belt, and means forming a source of high potential to be impressed across said spaced discharge-controlling means, and means supporting said source between the upper and lower sides of the belt.

6. In electrical treating apparatus, in combination, a conveyor belt supported by spaced drums and having an upper product-carrying side and a lower return side spaced from the upper side, spaced discharge-controlling means, one above the upper side of the belt and the other underneath the upper side of the belt, a high voltage transformer for impressing high voltage across said discharge-controlling means and positioned between the upper and lower side of said belt, the lower side of said belt passing overidler means whereby the spacing between the two sides of the belt is increased to accommodate said transformer.

'7. In electrical treating apparatus, in combination, a conveyor belt supported by spaced drums and having an upper product-carrying side and a lower return side spaced from the upper side, spaced discharge-controlling means, one above the upper. side of the belt and the other underneath the upper side of the belt, means positioned between the upper and lower sides of said belt and forming a high voltage source impressed across said discharge-controlling means and having a high voltage insulating terminal construction, and means whereby the discharge-controlling means underneath the upper side of the belt is supported by said terminal construction.

8. In electrical treating apparatus, in combination, a conveyor belt supported by spaced drums and having an upper product-carrying side and a lower return side spaced from the upper side, a frame supporting said spaced drums and having an upward extension, a motor supported by and grounded to said extension, electrode means above the upper side of said belt and driven by said motor and being grounded to said frame, high voltage electrode means underneath the up per side of said belt, and insulating means supporting the last-mentioned electrode means.

9. An apparatus like that of claim 8 in which the insulating supporting means insulatingly carries the high potential to the electrode means supported thereby.

10. An apparatus like that of claim 8 in which the motor-driven electrode means is in the form of electronic conduction means.

11. An apparatus like that of claim 8 in which the motor-driven electrode means is in the form of a depending electronic conduction tube inclined away from its direction of travel.

FRANKLIN S. SMITH. 

